System for eliminating crossfire in telegraphic circuits



0ct. l, 1940. w. D. CANNON 2,216,545

SYSTEM FOR ELIMINATING CROSSFIRE IN TELEGRAPHIG CIRCUITS Filed March 50. 1938 '7 Sheets-Sheet l v @Mx 0d. l, 1940. w. D. CANNON 2,216,545

SYSTEM FOR ELIMINAITNG CROSSFIRE IN TELEGRAPHIC GIRCUITS lFiled March so. 19:58

'7 Sheets-Sheet 2 W11., fawn Oct. 1, 1940. w. D. CANNON 2,216,545

SYSTEM FOR ELIMINATING CROKSSFIRE IN TELEGRAPHIC CIRCUITS Filed March 30, 1938 '7 Sheets-Sheet I5 n.f. Cannon l oct. l, 1940. W D CANNON 2,216,545

SYSTEM FOR ELIMINATING CROSS'FIRE' IN TELEGVRAPHIC CIRCUITS Filed March 30, 1938 '7 Sheets-Sheet 4 Oct. 1, 1940. W D CANNON 2,216,545

SYSTEM FOR ELIMINATING CROSSFIRE 1N TELEGRAPHIC CIRCUTS Filed March 30, 1938 7 SheetS-Sheet 5 Oct l, 1940. w. D. CANNON SYSTEM FOR ELIMINATING CROSSFIRE IN TELEGRAPHIC CIRCUITS Filed March 30, 1938 7 Sheets-Sheet 6 Oct. 1, 1940. w. D. CANNON SYSTEM FOR ELIMINATING CROSSFIRE IN TLEGRAPHIC CIRCUITS 7 Sheets-Sheet 7 Filed March 30, 1938 Patented Oct. 1, 1940 UNITED STATES PATENT OFFICE SYSTEM FOR ELIDIINATING CROSSFIRE IN f TELEGRAPHIC CIRCUITS Application March 30,

20 Claims;

This invention relates to a system designed to eliminate Crossfire between parallel conductors of communication circuits and may also have application to the elimination of cross talk and interference in other types of circuits.

Interference or Crossfire between parallel circuits comprises the major cause of signal loss on grounded telegraph circuits operated over heavy pole line leads. The interference levels in the various circuits' are different, due to the nonuniform mutual exposures. At any terminal this Crossre interference is roughly divisible into two portions; that due to the local transmitt'eiis, known as sending-end crossfire and that due to the distant end transmitters, known as far end Crossfire. The near end Crossfire ordinarily predominates. Since most telegraph circuits terminate in a duplex arrangement of apparatus, it is common to provide interconnections between the articial line terminals of the duplex apparatus for the various wires so that each terminal set sends a correcting pulse through a properly adjusted network to the sets located on all of the neighboring wires. If the correcting system includes all of the conductors of the pole line and the correcting networks are properly designed, a very satisfactory degree of neutralization of the sending-end Crossfire may be effected.

Receiving-end Crossfire, however, may only be neutralized by introducing into the signaling portion of the disturbed line or the terminal equipment, a neutralizing impulse from the disturbing line of proper phase and magnitude to neutralize the intercepted crossre disturbance. It is common to perform this correction by sending a neutralizing pulse into the disturbed line from the transmitter of the disturbing line either by means of an auxiliary relay or through a transformer coupling. These methods involve either relatively low impedance shunts from the line to ground or a low impedance coupling between the lines and are thus objectionable because of their effect on signal transmission.

I'he object of the present invention is to provide a circuit arrangement for substantially eliminating receiving-end telegraph crossre or both receiving and sending-end crossfire, which functions with negligible impairment to the transmission of telegraph signals. For this purpose I have disclosed herein a crossfire neutralizing system employing therminonic tubes which possess the advantage of very high impedance input and relatively high impedance output circuits, whereby it is possible to provide the intere 1938, Serial No. 198,997v (Cl. 178-69) connections between lines without serious eiect upon the transmission of signals.

Otherandy further objects of this invention will be apparent from the following description,

when read in connection with the accompanying drawings, in which- Figure l is a diagram illustrating an embodiment of my invention wherein the input circuit of a thermionic tube is adjustably connected to each line via a high impedance and the respective output circuits are connected to each of the other lines in parallel. Y l v Figure 1a illustrates a simple network which may be employed to interconnect the vvarious lines.

Figure 2 shows a crossre neutralizing system wherein the output of each thermionic tubeis connected to an individual line wire while the input is connected tothe disturbing vlines in combination. l

Figure 3 shows the application of my Crossfire neutralizing system in association with a power induction system such as disclosed in my application, Serial No. 28,359, nled June 25, 1935. Figure 4 illustrates the application of my crossfire neutralizing system to an arrangement wherein the wires are divided into quads; the ltwo conductors of each pair being neutralized for each other andthe two pairs being then neutralized against' each other; the quad also constituting a third unit to" be neutralized against the neighboring quads.

Figure 5 shows a Crossfire neutralizing arrangement for nullifying the receiving-end Crossfire in a system having several adjacent circuits, while the sending-end crossre is neutralized by the usual anti-induction networks connected to theartificial lines oi said several circuits.

Figure 6 discloses an arrangement for supplementing the neutralization obtained in the manner shown in Figs. 1 and 2, by introducing an additional neutralizing pulse at the sending end of such value as' to provide the yrequisite shape and amplitude when it reaches the distant end, thus neutralizing the receiving-end crossre.

Figure 7 shows an arrangement'for picking up a neutralizing potential at the receiving' end of each wire for introduction into the receiving apparatus of the adjacent Wires.

Figure 8 shows the manner in which the ysystem adapted to neutralize both sending-end and receiving-end interference, such as disclosed in Figs. 1 and 2, may be combined Withan additional correction, using a system such as that shown in Fig. 6.

Figure 9 shows an arrangement similar to that of Fig'. 2 but including additional means for neutralizing sending-end Crossfire via the articial line connections of the terminal duplex telegraph sets.

Figure 10 shows an arrangement for picking up a neutralizing potential at the receiving end of each wire in a manner similar to that of Fig. '7, but which is introduced through transformer directly into the adjacent wires.

Figure l1 illustrates the adaptation 0f my Crossfire neutralizing arrangement to a system embodying a plurality of adjacent circuits comprised of pairs of wires rather than single wires, as in Fig. 2.

Figure 12 illustrates the application of my neutralizing system toI a group of adjacent circuits in such a manner that the possibility of singing or feedback from the output to the input circuits of the amplifiers is substantially reduced. l In Fig. 1 I have illustrated a crossre neutralizing arrangement which may be adapted to neutralize bothsending-end and receiving-end interference, wherein the input circuit of a thermionic vacuum tube for each line is connected via a high impedance 5, and the respective output circuits are then adjustably connected to each of the other lines through suitable networks N The vacuum tube units serve to provide a oneway coupling from each line as a disturbing line lto the lother lines as disturbed lines, at the same time operating to reverse the phase of the correcting -pulse by 180 to thereby neutralize the disturbing potentials. The input impedances 5, connected from each line to ground are of high value and are therefore negligible in their effect on the line characteristics, while the networks N, which interconnect the various; lines are also high in value, so that they are productive of but small mutual interference. This mutual interference, due to the networks N, is itself neutralized through the adjustment of the neutralizing system, which is designed to have a sufficient excess of capacity to neutralize the interference which it introduces of itself. The networks N may be of any suitable nature which will admit -a neutralizing voltage of proper magnitude and phase. Usually a simple network such as that shown in Fig. la has been found suicient. Resistancecapacity output coupling for the tubes is shown, but'an'y other of the common` types of coupling may be used instead, which will handle the requisite power and frequency range.

Thus when an interfering voltage is impressed upon the line 3, a fraction of said voltage is obtainedby selecting a portion of the drop across the high impedance 5, which is impressed upon the input of amplifier tube 1, and causes the output of the tube to impress a compensating voltage on the lines I and 2, of the proper phase and amplitude to neutralize the voltage induced in said lines, due to said interfering voltage in line 3, and in a similar manner disturbing voltages induced in lines I and 3 by line 2, and in lines 2 and 3 by line I, are neutralized by the tubes 8 and 9 respectively. Thus the neutralizing system acts mutually upon all of the wires.

The neutralizing arrangement disclosed in Fig. 2 differs from that shownin Fig. 1 in that the outputv of each tube is connected to an individual line, while the input is connected to the disturbing lines in combination. I have illustrated pentode type tubes which have a high gain and high plate impedance, but other types of tubes may be used.

The crossre neutralizing system disclosed herein is useful in connection with certain types of power` induction neutralizing systems, such as that disclosed in my prior application issued May 23, 1939, as Patent No. 2,159,927. In power induction neutralizing transformers as shown in said patent, a control wire is used to pick up the disturbing current and apply it in proper phase and magnitude to neutralize the like interference intercepted by the disturbed signal conductors. It is apparent that telegraph crossre picked up by the control wire will also tend to be introduced into the other conductors. It will be seen that a certain portion of this cross-fire in the control wire may be utilized in the neutralizing amplifier to neutralize the like disturbance in the other wires which traverse the neutralizing transformer. However it is desirable to eliminate all telegraph disturbances in the control wire over and above that which functions to eliminate the crossre in the other wires. In Fig. 3, I have illustrated the use of the crossre neutralizing system disclosed herein, to neutralize the crossre in the control wire 6 of the power neutralizing system, but which is so adjusted that a portion of said crossre, suicient to neutralize the Crossfire in the telegraph lines, is permitted to remain in the control wire.

In Figure 4 I have shown a neutralizing arrangement embodying my invention in which the communication line wires are divided into quads. The two conductors of each pair are neutralized for each other and the two pairs are then neutralized against each other, while the entire quad constitutes a third unit to be neutralized against neighboring quads.

The operation of the neutralizing arrangement shown in Figure 4 will be evident from the previous description of Figure l. Thus the disturbing voltages in line I impressed upon the input of tube la, cause the output of said tube to transmit a neutralizing voltage through the conductor I2 to the opposite conductor 2. Likewise disturbing voltages in line 2 transmit neutralizing voltages through conductor I3 to line I. In a similar manner disturbing voltages between lines 3 and 4 are mutually neutralized.

The combined disturbing effect of the pair of lines I and 2 is then neutralized with respect to the pair of lines 3 and 4. Disturbing voltages of the pair of lines I and 2 are impressed through the conductor I4 upon the input of tube 1C, thereby causing the output of tube Ila to transmit neutralizing impulses through the conductor I6 to the pair of lines 3 a-nd 4. In -a similar manner disturbances in the combined lines 3 and 4 are impressed through the conductor I1 upon the input of tube 7d and cause the output of tube 8b to transmit neutralizing voltages through the conductor I8 to the pair of lines I and 2. In a similar manner the disturbing effects of the quad consisting of the two pairs of wires are neutralized in a neighboring quad by neutralizing voltages transmitted thereto through the conductors I9 and 20e, while a vneutralizing voltage from the other wires is received via conductor 20. It will be seen, therefore, that the neutralizing system acts severally or reciprocally upon all other wires.

For most of the amplifiers a single stage of amplification is sufficient to provide a suitable neutralizing potential but with some circuits the second stage is necessary in order to preserve the 180 phase relation, This need not be the case, however, if transformer coupled amplifiers are used.

associated with lines 2 and 3, these impulses being transmitted through the networks N1 connected to said conductor and causing a voltage drop across the high impedance 5Ib, a selected part of which is impressed upon the input of tube 46. In this manner the tendency both to receiving-end crossfire and sending-end crossre is effectively nulliiied in line I. In a similar fashion reciprocal connections via other networks N and N1 to wires I, 2 and 3, serve to neutralize the crosslire induced in lines 2 and 3.

In Fig. I have shown an arrangement for neutralizing the receiving-end crossiire in communication lines by introducing the neutralizing voltage directly into the line, instead of into the receiving instrument, such as shown in the arrangement of Fig. '7. kThe operation of the arrangement of Fig. 10 will be obvious from the previous description of Fig. 7. 'Ihe disturbing crossre induced in line I by the currents received in lines 2 and 3 is nulliiied by voltages induced in the secondary coils of bridge transformers T13 and T14. The voltages induced in the secondary coils s1 of said transformers produce a current through networks N, conductor 'ID and resistance 65. A selected portion of the drop across said resistance is applied to the input of tube 62 which causes the transformer T10 in the output of said tube to introduce a voltage of the proper magnitude and phase to neutralize the receiving-end Crossfire in the line I.

Since the frequencies involved are rather low, the necessarily large inductance of the transformer T10 is harmful to telegraph transmission. In order to neutralize this impedance, I introduce tertiary windings ain the transformer which feed back into the input of the ampliiier 62, a potential sunicient to overcome the losses introduced into the line circuit by the main line windings b. It will be evident that the sending-end Crossfire in the arrangements shown in Figs. 7 and 10 may be neutralized using in addition the sending-end neutralizing means shown in` Figs. 1, 2 or 5.

Interference neutralizing systems are preferably set up at each end of the line, where they provide protection for the terminal apparatus. Due to the high impedances of the interconnections, the mutual coupling between wires in the arrangements herein described is inappreciable, yet the wires approach a freedom from interference normally possessed only by isolated wires or metallic circuits.

'I'he vacuum tubes for the neutralizing system herein described, should preferably have a relatively high power output and should be of high impedance inasmuch as they are connected between the various lines or between the lines and ground. Pentode types of tubes have proved very satisfactory for this purpose. In some of the systems described there is an apparent coupling between the input and output of the various amplifiers, which may be expected to produce undesirable oscillation. In most instances, this tendency is negligible under conditions of proper adjustment.

I have not illustrated the terminal apparatus in Figs. 1 to 4 inclusive but it is to be understood that the wires are available for either one way or two way telegraph, or for other purposes, without substantial impairment to transmission. In some cases when duplex terminal sets are used it may be desirable to include in the artificial line passive networks to balance the networks N or other elements connected to the real lines.

- In the arrangements previously described the neutralizing system has been applied particularly for neutralizing transient disturbances but it is also adapted for neutralizing disturbances of a continuous type. For example, it may be employed for neutralizing interference, such as .crosstalk, in telephone or other voice frequency or higher frequency circuits induced by the mutual coupling between the Wires. This involves merely the adaptation of the arrangements previously described to circuits comprised of pairs of wires rather than single wires.

In Figure 11 I have shown my neutralizing system applied to a group of adjacent circuits, each composed of a pair of wires. This arrangement is analogous to that shown in Fig. 2 and its operation will be readily understood from the description of that figure. Transformer coupling of the neutralizing system to the line circuits is indicated merely because of its economy and convenience. Obviously resistance coupling may be used and it would then be necessary to employ push-pull amplifiers as shown in Fig. 9, if common grounded batteries are to be used. Otherwise the pairs would suffer an unbalance to ground.

I have illustrated in Figure 12 the application of my neutralizing system to a group of conductors in such a manner that the possibility of singing or feedback from the output to the input circuits of the amplifier is substantially reduced. In this figure the three line circuits I, 2, and 3 terminate in the balanced hybrid coils of standard 22 type telephone repeaters. Such a repeater is illustrated in Patent 1,227,114, and need not be further described. Supplementary Windings c and d are added to each hybrid coil for the purpose of picking up potentials which may be applied in conjugate fashion for neutralizing the disturbances induced in the other circuits. As indicated, the windings associated with each pair but one, are joined in parallel to the input of an amplier whose output is then connected to the input of an amplifier whose output is then connected to the transformer T22 which is connected across the bridge points of the hybrid coil of the remaining pair. Since the supplementary windings and the transformers T22 bear a conjugate relation to each other, the input circuits of all the amplifiers will be entirely independent of the output circuits of all the amplifiers. It will be understood that only one-half of each repeater is shown. 'Ihe second half would be similarly equipped for neutralizing the interference of the succeeding line section.

The neutralizing system of the invention may also be applied to regular 4-wire telephone circuits, such as are illustrated in Patent 1,352,786. In the 4-wire system, however, two neutralizing groups will be required inasmuch as the outgoing or sending currents are confined to one pair while the incoming or receiving currents are confined to the other pair. For neutralizing near end, or sending end, crosstalk it will be necessary to separately neutralize the interference from each sending pair into each of the adjacent receiving pairs, While a second group as in Figure 11 will be required to mutually neutralize the interference between all of the receiving pairs. Adaptations of the various methods previously illustrated to 4- wire circuits will be evident to engineers.

I claim:

1. In a communication system comprising several adjacent line circuits wherein different levels of interference are produced, due to non-uniformv mutual exposures, themethod of nullifying crossiire between said several' circuits, which consists in selecting a portion of each 'currentimpulse transmittedover. the respective lines, dividing said lines into a plurality of groups,v separately amplifying theselected impulses from each ofsaid groups, and supplying said ampliiied impulses mutually and reciprocally to all of the line circuits. l t i 2. In a communication system comprisingseveral adjacent line circuits wherein dierent levels of interference'are produced, due to non-uniform mutual exposures, lthemethod of nullifying crossiire between said .several circuits, which consists in deriving a selected portion of each current impulsetraversing the respective lines,.dividing said lines into a plurality of groups, separately amplifying the selected impulses from .each of said groups, and mutually `and reciprocally impressing the same upon' all of .the line circuits. i

3..',Ina telegraph-signaling system comprising a plurality of adjacent line circuits, ,the methodj of nullifying` receiving-end `and, sending-endA `crossfire between the respectivelinecircuits wherein dierent levels of interference are produced, due to .non-uniform mutual exposures, which consists in amplifying inductively derived portions of the signaling impulses received over any one of said respective circuits and applying the same mutually fand reciprocallyto the line conductors of all'of the other circuits, and applying ampliiied v portions of conductively derived impulses transmitted overany line mutuallyand reciprocally 1to all of the other lines of the system.

4. Anelectric system comprising a plurality of adjacent transmission-line circuits having different levels of interference, due to non-uniform mutual exposures, means for eliminating mutual interaction between said lines comprising a separate amplifier individually associated with each line and having its input connected to its respective line circuit and l impedance networks connecting its output to all of the other lines, whereby the input energy is always free of the energy of that line to which the output of said amplifier is connected.

5. An electric system comprising a plurality of adjacent transmission line circuits having different levels of interference, due to non-uniform mutual exposures, means for eliminating mutual interaction between said lines comprising a separate amplifier associated with each line and connected to its respective line circuit via its output, and shaping networks connecting lall of the other remaining line circuits lto its input.

6. In a communication signaling system embodying a plurality of adjacent transmission line circuits and having terminal equipment provided with transmitter and receiver adapted to separate the incoming and outgoing currents, means for eliminating mutual interference between said line circuits, comprising an amplifier associated individually with each line and having its output connected inductively to the transmitter of its respective line, and shaping networks connecting the input of the respective ampliers to the transmitters of all of the remaining line circuits.

'7. In a communication system a plurality of line circuits having different levels of interference, due to non-uniform mutual exposures, a

erallyto thereby nullify the receiving endcrossf re and a portion ofthe sending end crossrefin' all of said lines, and correspondingly interconnecting the artificial lines of said circuits toth'ereby nullify the remaining sending end Crossfire. 9. `In a communication system embodying a plurality of adjacent circuits having different levels of interference,r ldue .to non-uniform mutual exposures, and having terminal equipment'adapt-- ed to separate the .incomingand outgoing-.curirents, the `method of neutralizinginterference between said circuits (due` -to incoming currents which comprisesthefselection from eachfwire of a portion of the received current, separately arnplifying saidcurrents,'and applying-saidampliiied currents -mutually and'reciprocally to the line conductors of each ofthe remaining circuits. 'ffl l0. In a communication system embodying'a plurality of ladjacent circuits and having terminal equipment` adapted to separate the incoming and outgoing currents, the v"method of 'neutraliing interference` between said circuits ywhich comil prises theselectionfrom-each wire'of a portionfof the received currents therein, .separately amplify-1` ing said. .currents, a'ndfapplyingsaid' amplified currents mutually and reciprocally to impedances connected to the line conductors of all of the other circuits, and additional means for neutralizing the effect of said impedances upon said line circuits. r

11. In a telegraph signaling system comprising a plurality of adjacent line circuits having different levels of interference, due t-o non-uniform mutual exposures, the method of nullifying receiving-end crossiire between adjacent circuits when signaling impulses are impressed upon any one of said circuits, which consists in producing jacent circuits when si-gnaling impulses are impressed upon one of said circuits-which consists in inductively deriving impulses at the receiving end of a crcuit when signaling impulses are received thereover, amplifying said derived impulses and inductively impressing them upon the circuit of the receiving instrument.

13. In a system for neutralizing current induction in a plurality of adjacent line wires which traverse the coils of a compensating transformer,

and provided with a control Wire external to said transformer and exposed to the same induction with said line wires, said control wire being connected to a coil of said transformer, of means for the elimination of crossre between the line wires and .the control Wire, comprising a thermionic tube provided with input and output circuits, said tube having its input circuit connected to' said wires 'and-its. output circuit con-y nected to said control wire.

14. In a communication signaling system embodying a plurality of adjacent transmission circuits, an arrangement for the elimination of mutual interference between said circuits, which consists in means for neutralizing interference between the conductors of separate pairs of said circuits, means for neutralizingY interference betweenone and another of said pairs of circuits, and means for neutralizing interference between said combined pairs considered as a quad and another; like quad consisting of a similar group of two pairs which-have been likewise neutralized against each other. v

15. In a telegraph system embodying a plurality of adjacent transmissionwires, means for eliminating crossre, comprising a seriesof thermionic tubes provided with input and output circuits, each'tube having one of said circuits connected to only one of said transmission wires and its otherl circuit connected to all of the remaining wires.

- 16. Ina telegraph system embodying a plurality of adjacent transmission Wires, means for eliminating crossracomprising a series of .thermionic tubes provided withinput and output circuits, each tube having its input circuit connected to only one of said transmission wires and its outto all of the remaining 18. In a communication system comprising several adjacent line circuits, each circuit embody? ing a pair of conductors, the method of nullifying Crossfire between said several circuits, which consists in combining selected portions of the current impulses simultaneously transmitted over all but one of said circuits, amplifying the resultant current impulse and supplying said resultant to said one circuit, and simultaneously applying said operation to each of the several individual line circuits.

19. An electric system including several adjacent transmission circuits wherein different levels of interference are produced, due .to non-uniform mutual exposures, each circuit embodying a pair of conductors, means for eliminating mutual interaction between said circuits, comprising separate ampliners, each connectedvto its respective circuit via its output, and impedance networks interconnected to the other circuits of the systems, connected to the input of the amplifier.

20. In an electric system including a plurality of adjacent transmission circuits, each of said circuits embodyingv a pair of conductors, the method of neutralizing interference between said circuits, due to incoming currents, comprising inductively selecting from each said circuit a portion of the received current, amplifying said portions jointly from all of said circuits but one, applying the amplied current vto said last named circuit in conjugate relation to `the inductively selectedpor-tion andsimultaneously applying the same operation to each of said circuit-s.

WILLIAM D. CANNON. 

